Coiled steel tubing finds a number of uses in oil well operations. For example, it is used in running wireline cable down hole with well tools, such as logging tools and perforating tools. Such tubing is also used in the workover of wells, to deliver various chemicals and perform other functions.
Steel coiled tubing is capable of being spooled because the steel used in the product exhibits high ductility (i.e. the ability to plastically deform without failure). The spooling operation is commonly conducted while the tube is under high internal pressure which introduces combined load effects. Unfortunately, repeated spooling and use causes fatigue damage and the steel coiled tubing can suddenly fracture and fail. The hazards of the operation and the high personal and economic cost of failure in down time in fishing operations forces the product to be retired after relatively few trips into a well. The cross section of steel tubing expands during repeated use, causes reduced wall thickness and results in lower pressure allowables and higher bending strains.
It is desirable to provide a non-steel coil tubing which is capable of being spooled and which does not suffer from the defects of steel tubing.